Battery technology has undergone considerable change in recent years in response to demands for higher reliability, greater capacity per unit weight or volume, longer shelf life and greater cycle life. This has been due to market demands for more portable equipment (e.g., telephones, tools, computers, etc.) as well as back-up power sources for a variety of devices including memories and other components associated with computers.
A particularly attractive type battery for many applications is a nonaqueous battery, especially those featuring lithium as the active material in the negative electrode. Such battery cells feature very high cell potential and low weight density and result in cells of high energy density (see, for example, High Energy Batteries, by R. Jasinski, Plenum Press, New York, 1967, pp. 140-144).
Exceptionally good active materials for the positive electrode of lithium non-aqueous batteries are niobium diselenide, niobium triselenide, and niobium trisulfide (see for example, U.S. Pat. No. 3,864,167 issued on Feb. 4, 1975 to J. Broadhead et al, incorporated herein by reference). These electrode materials not only have high energy density, good charge and discharge characteristics (cycle performance) and good stability, but also are compatible with a large variety of electrolyte systems. Tests carried out on lithium cells made with these positive electrode materials (especially with niobium triselenide) confirm the advantages outlined above.
Electrodes comprising NbSe.sub.3 can be fabricated by providing a thin Nb foil and reacting it with Se vapor. The resulting fibrous sheet of NbSe.sub.3 is then rolled onto a metal grid that serves as current collector. The above process has several shortcomings, including relatively high materials cost, and relatively long reaction time. Furthermore, it is generally difficult to produce thin sheets of active material of uniform thickness and morphology by means of the prior art technique. Another procedure involves reacting niobium powder with chalcogenide vapor under conditions where the desired niobium chalcogenide is formed. For niobium triselenide, the conditions involve heating the niobium powder in the presence of selenium to a temperature of about 625.degree.-680.degree. C. Often, a two stage heating process is preferred; first heating to about 580.degree. C. for about 15 hours and then heating to about 680.degree. C. for 15 hours. (See for example, the recently filed application entitled "Non-Aqueous Cell Comprising Niobium Triselenide" with inventors Wei-Chou Fang and Brijesh Vyas filed Sept. 14, 1988 with Ser. No. 244,218U.S. Pat. No. 4,489,145). Niobium-selenium compounds are discussed in a paper by V. E. Fedorov et al., Russian Inorganic Materials, 20, 935 (1984).
In order to increase the commercial value of using chalcogenides such as NbSe.sub.3 as the active positive electrode material in non-aqueous cells, it is desirable to reduce the cost of fabricating cells with chalcogenide active material and to make the fabrication procedure more easily adaptable to mass production. In particular, it is desirable to find a synthesis procedure for NbSe.sub.3 active electrode material that is less expensive, that can be used to produce thin sheets of active material of uniform thickness, and that is less cumbersome and/or more easily adapted to mass production under manufacturing conditions than those known to the prior art.